Mice infected with MMTV (mouse mammary tumor virus) resulted in a hot spot insertion in the Notch 4 locus, which led to the constitutive expression of NOTCH-4 and its target genes, truncation and activation of NOTCH-1 as an oncogene, and eventual development of mammary adenocarcinoma [10, 11]. Here, NOTCH4 is linked to breast adenocarcinoma.